Transistor ignition system



1965 s. B. ROBBINS 3,200,803

TRANSISTOR IGNITION SYSTEM Filed Aug. 6, 1962 /03 INVENTOR. 1 z SAMUEL 5. ROBE/N5 l 94 I W BY 0,92%

A TTORNE) United States Patent 3,206,8il3 'IRANSISTGR IGNITIUN SYETEM Samuel B. Robbins, Rochester, Mich, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Aug. 6, 1962, Ser. No. 2l5,tl8 ll 12 Claims. (El. 123-443) This invention relates to an ignition system for internal combustion engines and more particularly to an ignition system wherein a semiconductor such as a transistor controls the current flow in the primary winding of the ignition coil.

One of the problems encountered in the use of transistor ignition systems is the destructive kick back voltage which comes from the primary winding when the current flow to the primary winding is interrupted and which under certain conditions can destroy the transistor that controls primary current. In some instances, diodes and combinations of diodes and resistors have been used to block the kick back voltage or to provide a current path around the transistor for the energy developed by the kick back voltage.

One of the objects of this invention is to provide an ignition system wherein the kick back voltage is used to build up energy for firing a spark plug. This object is accomplished by continuously reversing the current flow through the primary Winding of the ignition coil so that when an inverse kick back voltage occurs, the current flowing through the primary Winding from a DC. source is in the same direction as the current developed by the kick back voltage. In this system, transistors are used to control the current flow through the primary winding and the transistors are connected to provide current flows for the primary winding that are alternating in opposite directions.

Still another object of this invention is to provide a completely breakerless ignition system which is capable of causing a reversal in current through the primary winding of an ignition coil during operation of the ignition system.

A more specific object of this invention is to provide a transistor ignition system wherein the conduction of the transistors is controlled by a magnetic pick up device which has a center tapped pick up coil and a rotor which rotates relative to the pick up coil and which has sectors of alternate opposite magnetic polarities.

Another object of this invention is to provide a voltage pulse generating device which can be used to control a semiconductor ignition system or the like and which has an AC. output that is substantially a square wave. This type of output voltage is useful since it can instantaneously reverse the bias voltage applied to one or more semiconductors such as transistors to cause them to switch sharply from one condition to the other. This object is carried forward by providing a magnetic rotor which has radially extending pole teeth that cooperate with the pole faces of a core. The rotor pole teeth have the same width and are spaced from each other by this same width. In addition, the pole faces of the core are spaced this same width and the pole faces themselves have the same width. As a result of this, the voltage output is an alternating square wave which is capable of sharply switching semiconductors such as transistors.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIGURE 1 is a schematic circuit diagram of an igni' tion system made in accordance with this invention.

3.2%,8h3. i atentecl Aug. 17, 1965 FIGURE 2 is a top view of a magnetic pick up device for controlling the ignition system of FIGURE 1.

FIGURE 3 is a side view of the magnetic pick up de vice illustrated in FIGURE 2.

Referring now to the drawings and more particularly to FIGURE 1, the reference numeral 10 designates an internal combustion engine which has a plurality of spark plugs 12 for firing the combustible mixture of the engine. In the particular instance, there are eight spark plugs for an eight cylinder engine but it will be apparent to those skilled in the art that the number of spark plugs can vary with the number of cylinders in the engine. The spark plugs 12 are connected with the electrodes 14 on a conventional distributor cap generally designated by reference numeral 16. A rotor member 18 is driven in synchronism with the engine and is driven in synchron ism with a rotor member 20 of a magnetic pick up which is more fully described heereinafter. The rotor contact 18 is electrically connected with a lead wire 22 coming from the secondary winding 24 of an ignition coil 26. It is seen that the opposite side of the secondary winding 24 is grounded and that the ignition transformer 26 has a primary winding 28.

The current flow through the primary winding 28 is controlled by a plurality of semiconductor devices which in this case take the form of PNP transistors 39, 32, 34 and 36. It can be seen that the emitter electrodes of transistors 30 and 34 are connected with a lead wire 38. The base electrode of transistor 30 is connected with a junction it while the base electrode of transistor 34 is connected with junction 42.. The collector electrode of transistor 3b is connected with junction 44 and it can be seen that this junction is connected to one side of the primary winding 28 by a conductor 46. The collector electrode of transistor 34 is connected with junction 48 and this junction is connected with the opposite side of primary Winding 28 via a conductor 58).

The emitter electrode of transistor 32 is connected with junction 54 While the collector electrode of this transistor is grounded through junction 52. The base electrode of transistor 32 is connected with junction 54 on a lead wire 56. The emitter electrode of transistor 36 is connected to junction 48 whereas the collector electrode of this transistor is grounded at junction 52. The base electrode of transistor 36 is connected with junction 60 via the lead wire 58.

Ignition power for the ignition system is supplied by a DC. voltage source 64 which is illustrated as a battery. It will of course be appreciated that the battery supplies ignition power during cranking of the engine but that ignition power thereafter is supplied by a generator which also charges the battery in a motor vehicle system. In anycvent, ignition power is supplied to the system either from the battery or from a generator through a conduct-or 66 and a manually operable ignition switch 68. I A resistor 7i connects the junction with conductor 66 and another resistor 72 connects the conductor 56 with junction 54. A resistor 74 is connected between lead wires 66 and 33.

The conduction of transistors 30 through 36 is controlled by a magnetic pick-up device and a pair of PNP transistors 76 and 78. The emitter electrode of transistor i6 is connected with junction while the collector electrode of this transistor is connected with grounded junction 80. The base electrode of transistor 76 is connected with junction 82.

The emitter electrode of transistor 78 is connected with junction 42 while the collector electrode of this transistor is grounded at junction 80. The base electrode of transister 7% is connected with junction 84.

A resistor 86 connects the junctions 82 and 88 and another resistor 90 connects the junctions 88 and 84.

see-sees 3 It is seen that junction $3 is connected with junction 92 on the power supply conductor 66.

The magnetic pick up assembly for controlling the ignition system is illustrated in FIGURES 2 and 3. This magnetic pick up assembly includes a base M which rotatably supports a shaft 96 that is driven by the engine. The shaft 96 carries the rotor 24) which is formed of a nickel material and which has eight radially directed pole tips or arms which are magnetized with opposite polarities as is depictedin FIGURE 2. In other words, the arm or pole tip 100 has a south polarity whereas the arm or pole tip 102 has a north polarity. This sequence continues for the other six pole tips as is clear from an inspection of FIGURE 2. The nickel rotor is permanently magnetized by a suitable magnetizing fixture so that the pole tips are permanently magnetized in a manner illustrated in FIGURE 2. The rotor thus is a permanent magnet with the pole tips having alternate opposite magnetic polarities. The arcuate ends of the pole tips are the same circumferential length as the gaps between the pole tips. In the embodiment illustrated, each arcuate end of a pole tip and gap is one sixteenth of 'a circle for an eight cylinder engine but this of course would change to one twelfth for a six cylinder engine, one eighth for a four cylinder engine and so forth.

The pick up coil assembly is generally designated by reference numeral 104 and is supported on a timing plate ltid'which can be adjusted relative to the base 94.. This timing plate can be shifted around the axis of the shaft 96 by a suitable vacuum unit which is not illustrated and which would be connected with the intake manifold of the engine 10. The magnetic pick up assembly includes a laminated core 108 formed of magnetic material such as steel laminations. A coil Winding 11f is wound a on the core and this coil winding is center tapped at 112 as is apparent from FIGURE 1. This center tap is grounded by lead wire 114 illustrated in FIGURE 1 and in FIGURE 2. It is seen that the ends 108a and 1498b of the core 108 are arcuately shaped.

The pole faces 198a and 10% have the same arcuate cause a voltage to be induced in the center tapped coil winding 110. It can be seen that as the rotor rotates, the magnetic flux is continuously reversed in the magnetic core 108. In other words, the pole tip 162 is a north pole but when the rotor rotates so that pole tip 10%) aligns with core face 108a, the flux through the core 1% is reversed in direction from the direction of flux flow with the parts in the position illustrated in FIGURE 2. It will be appreciated that there are only short instants of time wherein during movement of the rotor with respect to the core when the rotor pole tips are not aligned with at least some part of the pole faces 108a and Itidb. During these instants, the field collapses and is instantly built up in the opposite direction This provides a. square wave voltage output which can sharply switch the transistors in a manner to be more fully described.

The operation of the ignition system of this invention will now be described. When ignition switch 68 is closed, the power line 66 is connected with one side of the direct current power source 64;. This biases the transistors 76 and '78 to their nonconductive states'since a positive voltage is applied to their base electrodes through junction 92 and resistors 36 and 88. It can be seen that the base current path for transistors 30 and 36 is through the emitter-collector circuit of transistor 76 and since this transistor is now off, the transistors 30 and 3d are turned ch in their emitter-collector circuits. The base current path for transistors 32 and 34 is through the emitter-collector circuit of transistor 73 and since this transistor is likewise turned ed, the transistors 32 and 3d are turned off. 1

As the rotor 2t} rotates, the voltage induced in the pick up coil will at certain positions of rotor 20 have a polarity as indicated in FIGURE 1 but this polarity will then be sharply reversed during continued rotation. This polarity thus continuously sharply reverses as the rotor 2d rotates.

. When the voltage induced in the coil winding 110 has the polarity shown in FIGURE 1, the base of transistor 76 is driven positive whereas the base or transistor 78 is driven negative. With the base of transistor 78 negative, 21 base current flows in transistor 78 to turn it on in its emitter-collector circuit. This completes a base current path for transistors 32 and 34 and they turn on in their emitter-collector circuits. A circuit may now be traced for supplying current to the primary winding 23 which is from junction 92, through lead wire 66, through resister 74-, through lead wire 33, through the emitter-collector circuit of transistor 54, through the primary winding 28 through lead wire 46, through the emitter-collector circuit of transistor 32 and then to ground via junction 52. his will cause a build up of current in the primary winding 28 with current flowing through this winding in the direction of the arrow indicated in FIGURE 1.

As the rotor 29 now rotates to reverse the flux in the core N8, the voltage induced in the coil winding 110 is sharply reversed from its polarity shown in FIGURE 1. This drives the base electrode of the transistor 73 positive to turn it off and therefore turn off transistors 32 and 34. At the same time, the base electrode of transistor 76 is driven negative so it now conducts. With transistor 76 conducting, there is a base current path for transistors 30 and 36 and a circuit can now be traced in a reverse direction through primary winding 28. This circuit is from lead wire 66, through resistor 74, through lead wire 38, through the emitter-collector circuit of transistor 34), through lead wire 46, through primary winding 23, and then through the emitter-collector circuit of transistor 36 to ground. It can be seen from the foregoing that as the rotor rotates, a pair of transistors shut off, for example, transistors 32 and 34, while the other pair of transistors 3t) and 36 turn on. The net effect of this is to break the circuit to the primary winding 28 for one direction'of current flow which previously has been building up and then to complete a circuit for the primary winding for current flow in an opposite direction. During reversal of current flow through the primary winding 28, a high voltage is induced in the secondary wind ing 24 which causes one of the spark plugs 12 to fire. The kick back voltage of primary winding 28 will be in the same direction as the next build up of current since the circuit for the primary winding is interrupted for one direction of flow but is then completed for another direction of current flow.

Theresistors 8t; and 38 are bias resistors for the base electrodes of transistors 76and 78 as are the resistors iii and 72 for the transistors 3@ through 36. The resistor 74 is a current limiting resistor.

The particular construction of the magnetic pick-up of this invention plays an important part in insuring correct operation of the system. Thus, by using a magnetic rotor having equally spaced pole tips and gaps and a complementary core with the same spacing, sharp switching action is attained with a square wave voltage output.

While the embodiments of the present invention as herein disclosed, constitute a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

I. An ignition system for an internal combustion engine comprising, an ignition coil having a primary winding and a secondary winding, a spark plug connected with said secondary Winding, first and second semiconductor switch means, a source of direct current, a first circuit for supplying current to said primary winding in one direction including said first semiconductor switch means, a second circuit for supplying current to said primary winding in a reverse direction including said second semiconductor switch means, and control means driven in synchronism with said engine for controlling the conductivity of said first and second semiconductor switch means in a predetermined sequence.

2. The combination according to claim 1 wherein the semiconductor switch means are transistors.

3. The combination according to claim 1 wherein the control means is a magnetic pick up device having a part driven by the engine.

4. The combination according to claim 1 wherein the control means is a magnetic pick up device which has a rotatable permanent magnet rotor and a tapped pick up coil.

5. An ignition system for an internal combustion engine comprising, a source of direct current, an ignition coil having a primary winding and a secondary winding, a spark plug connected with said secondary winding, a first transistor having emitter, collector and base electrodes, a second transistor having emitter, collector and base electrodes, a first circuit for supplying current to said primary winding in a first direction including the emittercollector circuit of said first transistor, a second circuit for supplying circuit to said primary winding in a second opposite direction including the emitter-collector circuit of said second transistor, and control means driven by said engine and connected with the base electrodes of said first and second transistors for causing said first and second transistors to turn on and oil in a predetermined sequence.

6. The combination according to claim 5 wherein the control means includes a magnetic pick up having a tapped pick up coil.

7. The combination according to claim 5 wherein the control means includes a magnetic pick up having a tapped pick up coil and a pair of transistors.

8. An ignition system for an internal combustion engine comprising, an ignition coil having a primary winding and a secondary winding, a spark plug connected with said secondary winding, a first transistor having emitter, collector and base electrodes, a second transistor having emitter, collector and base electrodes, at source of direct current, an energizing circuit for supplying current to said primary winding in one direction including the emitter-collector circuit of said first transistor, an energizing circuit for supplying current to said primary winding in a reverse direction including the emitter-collector circuit of said second transistor, a third transistor having emitter, collector and base electrodes, a fourth transistor having emitter, collector and base electrodes, means connecting the emitter electrode of said third transistor with the base electrode of said first transistor, means connecting the emitter electrode of said fourth transistor with the base electrode of said second transistor, means connecting the collector electrodes of said third and fourth transistors to one side of said source of direct current, magnetic pick up means having a tapped pick up coil, means connecting the base electrodes of said third and fourth transistors with opposite ends of said pick up coil, and means connecting the tap of said pick up coil with said one side of said source of direct current.

9. An ignition system for controlling current flow through the primary winding of an ignition coil comprising, a pair of output terminals adapted to be connected with the primary winding of an ignition coil, first semiconductor switch means, second semiconductor switch means, an input terminal adapted to be connected with a source of direct current, said first semiconductor switch means completing a circuit between one of said input terminals and one of said output terminals to provide a current fiow in one direction between said input terminal and one of said output terminals, said second semiconductor switch means being operative to provide a current path between said input terminal an another of said output terminals in a revesre direction, and control means adapted to be driven by an internal combustion engine for controlling the turning on and turning off of said semiconductor switch means in a predetermined sequence.

10. The combination according to claim 9 wherein the semiconductor switch means are transistors.

11. The combination according to claim 9 wherein the control means includes a magnetic pick up device including a tapped pick up coil.

12. The combination according to claim 9 wherein the control means includes a pair of transistors and a tapped pick up coil.

References (Iited by the Examiner UNITED STATES PATENTS 1,970,327 8/34 Louis 310156 2,852,589 9/58 Johnson 123-148 2,877,366 3/59 Carr 310-456 2,878,298 3/59 Giocoletto 123-148 2,953,719 9/60 Guiot 123148 3,034,018 5/62 Rosenberg 123148 3,087,090 4/63 Konopa 123-448 RICHARD B. WILKINSON, Primary Examiner, 

1. AN IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE COMPRISING, AN IGNITION COIL HAVING A PRIMARY WINDING AND A SECONDARY WINDING, A SPARK PLUG CONNECTED WITH SAID SECONDARY WINDING, FIRST AND SECOND SEMICONDUCTOR SWITCH MEANS, A SOURCE OF DIRECT CURRENT, A FIRST CIRCUIT FOR SUPPLYING CURRENT TO SAID PRIMARY WINDING IN ONE DIRECTION INCLUDING SAID FIRST SEMICONDUCTOR SWITCH MEANS, A SECOND CIRCUIT FOR SUPPLYING CURRENT TO SAID PRIMARY WINDING IN A REVERSE DIRECTION INCLUDING SAID SECOND SEMICONDUCTOR SWITCH MEANS, AND CONTROL MEANS DRIVEN IN SYNCHRONISM WITH SAID ENGINE FOR CONTROLLING THE CONDUCTIVITY OF SAID FIRST AND SECOND SEMICONDUCTOR SWITCH MEANS IN A PREDETERMINED SEQUENCE. 